A common problem with potable water systems which have an associated water heater is that once the tap, valve or faucet controlling the flow of the water from the heat source is turned off, the water which is left in the line between the valve and the heater container gradually cools over time. If a sufficient amount of time has elapsed before the hot water from that tap is again required, the user must wait until the cooled water within the line is evacuated through the drain and the line is once again filled with warm water. This wait can be frustrating as it can require up to several minutes for the line to be evacuated and again filled with warm water. This water is wasted down the drain and the user must wait to shower or wash his or her hands. This problem can be particularly troublesome for large, single story homes, which tend to be more spread out than multilevel homes, where the water heater can be great distances from the farthest tap. It is not uncommon to have to wait several minutes for the cooled water in the line to evacuate before the warm water arrives at the tap location. This is repeated over and over if the water is allowed to cool again prior to usage.
Several solutions to this problem have been tried in order to provide quick warm water at remote taps from the water heating device. One such solution is a recirculating system in which a return line is plumbed from the most remote tap back to the water heater source with a recirculating pump installed to provide a continuous flow of water. The flow ensures a supply of warm water contained in the plumbed line so that whenever the tap is turned on, warm water flows. This type of system is usually constructed with a controller so that when the temperature within the line drops below a certain point, the pump is automatically activated until the water temperature rises. This cycling continues as needed. Typical flow rates of these recirculating pumps are in the range of four gallons per minute. While this type of system does provide warm water in the supply line, it has several drawbacks. First, the system is expensive to install and maintain. In addition to the return line, an electrical pump is usually installed. The pump must be maintained and is subject to failures. Also, the pump creates flow at a relatively high rate which leads to premature plumbing failures from erosion corrosion. In addition, there is an increase in electrical costs associated with the pump and the additional load on the water heater. However, by far the largest drawback is the up front cost of installing such a system.
A second form of solution to this problem is a point source instant hot water device. Such devices are typically installed directly below the tap where the hot water is desired. The supplemental point source heating device is electrical and expensive to install. The point source also provides rapid hot water only to the single tap, while the recirculating pump and loop described in the previous paragraphs can provide rapid hot water to all taps and valves off the main trunk line. The point source device usually has a small storage capacity of several gallons and can be set to provide boiling water on command. The main drawbacks of such a device are the initial cost, installation requirements, energy costs, and localized effect to one tap or valve. Scalding of a user's hands can also be a concern.
A third form of device installed to provide warm water to the outlets is a convective circulating loop. This device operates on the principal that in a closed, recirculating loop warm water will rise and cool water will fall, providing a continuous recharge of warmed water into the loop, from which taps and valves are operated. This system is installed by running a return loop segment from the farthest hot water tap back to the water heater. A venturi is provided to initiate flow, and a check valve is included to prevent back flow of water in the return line when the cold tap is operated. This device helps to save water as there is no waiting for warm water to take a shower or wash hands. It is estimated that a typical family of four will waste from 7,000 to 14,000 gallons of water per year letting the tap or shower run to receive warm water. While the device does save water, the main reason people utilize the technology is not having to wait for the warm water, i.e., the convenience factor. Another benefit of the system is that it does not require electricity to operate. The flow loop is driven by natural convective forces. The plumbed return loop enters the cold water line just before the water heater device. While this device does keep the water line filled with warm water, there are several limitations and drawbacks. First, in order to operate, the return loop must be above the water heater. If the system is installed in a typical one-story slab home with the potable water plumbing installed through the slab, then the necessary rise of warmed water and fall of cooled water will not take place. The device is therefore limited to usage in multilevel homes with the plumbing occurring above the heated water source. Another disadvantage of the system is the cost of running the return loop line in an existing home. The return loop can be tricky as it must traverse through the attic or floor joists and drop down to the water heater location. The line must then be attached to the cold water inlet of the water heater. This installation requirement limits the applications to professional plumbers or only the most adept homeowners. The main hindrance to the technology is the cost of installing the return loop and the hassle associated with it.
All of the systems described above are costly to purchase and install. All typically require the services of a professional plumber for installation. The first two systems require electricity to operate, and the third system requires the plumbing to be above the heated water source to operate. Even with these drawbacks, large numbers of these systems are installed for the convenience of having rapid warm water at all taps.
No one method of providing rapid hot water to taps has been devised which is easy, economical to install, and works without electricity in all locations.